M describes distant metastasis (spread of cancer from one part of the body to another).

The TNM staging system for all solid tumors was devised by Pierre Denoix between 1943 and 1952, using the size and extension of the primary tumor, its lymphatic involvement, and the presence of metastases to classify the progression of cancer.[1] It has gained a wide degree of international acceptance for many solid tumor cancers, but is not applicable to diffused cancers such as leukaemia and is of limited use for other cancers such as diffuse lymphoma and ovarian cancer.[2]

For the T, N and M parameters exist subclassifications for some cancer-types (e.g. T1a, Tis, N1i)

Examples

Small, low-grade cancer, no metastasis, no spread to regional lymph nodes, cancer completely removed, resection material seen by pathologist: pT1 pN0 M0 R0 G1; this grouping of T, N, and M would be considered Stage I.

Large, high grade cancer, with spread to regional lymph nodes and other organs, not completely removed, seen by pathologist: pT4 pN2 M1 R1 G3; this grouping of T, N, and M would be considered Stage IV. Most Stage I tumors are curable; most Stage IV tumors are inoperable.

Uses and aims

Some of the aims for adopting a global standard are to:

Aid medical staff in staging the tumour helping to plan the treatment.

Enable facilities around the world to collate information more productively.

Since the number of combinations of categories is high, combinations are grouped to stages for better analysis.

Versions

It is crucial to be aware that the criteria used in the TNM system have varied over time, sometimes fairly substantially, according to the different editions that AJCC and UICC have released. The dates of publication and adoption for use of AJCC editions is summarized here; past editions are available from AJCC for web download.[4]

Edition 1 published 1977 and went into effect 1978

Edition 2 published 1983 and went into effect 1984

Edition 3 published 1988 and went into effect 1989

Edition 4 published 1992 and went into effect 1993

Edition 5 published 1997 and went into effect 1998

Edition 6 published 2002 and went into effect 2003

Edition 7 published 2009 and went into effect 2010

As a result, a given stage may have quite a different prognosis depending on which staging edition is used, independent of any changes in diagnostic methods or treatments, an effect that has been termed "stage migration." The technologies used to assign patients to particular categories have changed also, and by intuitive consideration it can be seen that increasingly sensitive methods tend to cause individual cancers to be reassigned to higher stages, making it improper to compare that cancer's prognosis to the historical expectations for that stage. Finally, of course, a further important consideration is the effect of improving treatments over time as well.